Radiant energy – Photocells; circuits and apparatus – Photocell controlled circuit
Patent
1996-04-25
1998-05-05
Westin, Edward P.
Radiant energy
Photocells; circuits and apparatus
Photocell controlled circuit
250226, 250214A, 250238, H01J 4014
Patent
active
057477914
ABSTRACT:
Devices for measuring one or more properties of a light signal is disclosed. More particularly the invention relates to devices for wavelength and power demodulation based on the use of quantum well electroabsorption photodiodes. In one aspect the invention provides and power and wavelength demodulation system based on a quantum well electroabsorption (QWEA) filtering detector. The input optical signal passes through an optical beam splitter with part of the signal input into a filtering detector which is a multiple quantum well electroabsorption (MQW EA) photodiode having a tunable bandgap and the other part into a reference detector. The input light signal is impinged on the QW diode perpendicular to the plane of the quantum wells. The output of filtering detector is amplified by an amplifier and the output of the reference detector is input into another amplifier. The output from reference detector amplifier serves as a measurement of the power of the input optical signal. The outputs of the amplifiers are input into an analog divider circuit where the signals are ratioed. A ratiometric voltage signal, V.sub.ratio, is obtained by ratioing the filtered output of filtering detector and the unfiltered reference output to provide optical intensity self-referencing (immunity to input power fluctuations). This V.sub.ratio output signal is continuously compared with a reference voltage signal, V.sub.ref, and the difference of V.sub.ratio and V.sub.ref is input into a feedback control circuit. The output voltage V.sub.out of the feedback control circuit is used to bias the QW EA photodiode so that in closed loop operation the OW EA photodiode is continuously wavelength tuned to maintain V.sub.ratio equal to V.sub.ref.
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Wavelength-selective voltage-tunable photodector made from multiple quantum wells; 3 pages, T.H. Wood, C.A. Burrus, A. H. Gnauck and J. M. Wiesenfeld, AT&T Bell Laboratories, Crawford Hill Laboratory, Holmdel, New Jersey 07733; D.A.B. Miller, D.S. Chemla and T.C. Damen, AT&T Bell Laboratories, Holmdel, New Jersey 07733 received 26 Apr. 1985; accepted for publication 14 May 1985.
Lee John R.
Schumacher Lynn C.
Westin Edward P.
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